CHAPTER 1 Introduction to Planet “Earth”

KEY QUESTIONS As you navigate this chapter, look for the answers to these key questions: • What is the nature of scientific inquiry? • What are the four principal oceans on Earth? • Where is the deepest part of the oceans, and have humans ever visited there? • How was early exploration of the oceans achieved? • Where did Earth and its oceans come from? • How do structure, composition, and physical properties vary within the deep Earth? (Chapter 2) • Did life on Earth begin in the oceans? • How old is Earth?

Overview 70.8% Earth covered by ocean Interconnected global or world ocean Oceans contain 97.2% of surface water Fig. 1.3ab

Pacific: Largest, deepest Atlantic: Second largest Indian: Mainly in Southern Hemisphere Arctic: Smallest, shallowest, ice-covered (??) Antarctic or Southern Ocean: Connects Pacific, Atlantic, and Indian, South of about 50o S latitude

Fig. 1.3cd

Early exploration Pacific Islanders traveled long distances Small islands widely scattered Fig. 1.5

Phoenicians: Mediterranean Sea, around Africa, British Isles Greeks:Pytheas reached Iceland 325 B.C., Ptolemy map 150 A.D.

The Middle Ages Vikings explored N. Atlantic Ocean Iceland and Greenland 9th and 10th centuries A.D. Leif Eriksson Vinland 995 A.D. Greenland, Vinland settlements abandoned by 1450 A.D.

The Age of Discovery in Europe 1492-1522 Search for new Eastern trade routes by sea Portugal trade routes around Africa (Prince Henry the Navigator) Europeans explore North and South America Columbus, Cabot Magellan and del Caño circumnavigate world

Voyages of Columbus and Magellan Fig. 1.7

Beginning of voyaging for science Capt. James Cook (1728-1779) Ships HMS Endeavour, Resolution, Adventure Mapped many islands in Pacific Systematically measured ocean characteristics Marine chronograph (longitude)

Cook’s voyages Fig. 1.8

01_G Charles Darwin Voyage of the Beagle 1831-1836

Sextant used to determine latitude Tools for navigation: Sextant used to determine latitude

01_E Harrison’s chronometer (1736) used to determine longitude (with accurate time-keeping). Prior to accurate chronometers, sailors used an hourglass.

Modern Oceanography: Research vessels, satellites, ROVs, moored sensors, submersibles (Alvin). Computers, mathematical models, GIS.

Nature of scientific inquiry Natural phenomena governed by physical processes Physical processes similar today as in the past Scientists discover these processes and Make predictions

Scientific method Observations Hypotheses Testing and modification of hypotheses Theory Probably true versus absolutely true Science is continually developing because of new observations

Evolution and natural selection Organisms adapt and change through time Advantageous traits are naturally selected Traits inherited Organisms adapt to environments Organisms change environments

Formation of Solar System and Earth Nebular hypothesis Nebula=cloud of gases and space dust Mainly hydrogen and helium Gravity concentrates material at center of cloud (Sun) Protoplanets from smaller concentrations of matter (eddies)

Nebular Hypothesis of Solar System Formation To view this animation, click “View” and then “Slide Show” on the top navigation bar. 21

Protoearth Larger than Earth today Homogeneous composition Bombarded by meteorites Moon formed from collision with large asteroid Heat from solar radiation Initial atmosphere boiled away Ionized particles (solar wind) swept away nebular gases

Protoearth Radioactive heat Spontaneous disintegration of atoms Heat from contraction (protoplanet shrinks due to gravity) Protoearth partially melts Density stratification (layered Earth)

Layered Earth Highest density material at center (core) Lowest density material at surface (crust) Earth layered Chemical composition Physical properties Fig. 1.12

Chemical composition Crust Low-density, mainly silicate minerals Mantle Mainly Fe and Mg silicate minerals Core High-density, mainly Fe and Ni

Physical properties Lithosphere Asthenosphere Cool, rigid, brittle Surface to about 100 km (62 miles) Asthenosphere Warm, plastic, able to flow From 100 km to 700 km (430 miles)

Fig. 1.13

Lithosphere Oceanic crust Underlies ocean basins Igneous rock basalt Average thickness 8 km (5 miles) Relatively high density 3.0 g/cm3

Lithosphere Continental crust Underlies continents Igneous rock granite Average thickness 35 km (22 miles) Lower density 2.7 g/cm3

Asthenosphere Upper mantle Plastic—deforms by flowing High viscosity—flows slowly

Isostatic adjustment Buoyancy Less dense “floats” higher than more dense Continental crust “floats” higher than oceanic crust on plastic asthenosphere

Fig. 1.14

Fig. 1.13

Age of Earth: Radiometric age dating Spontaneous decay of unstable nuclei. Based on uranium decay to stable lead isotopes measured in meteorites and old rocks, the Earth is about 4.6 billion years old. Example: 14C has 6 protons and 8 neutrons. It decays to 14N (7 protons and 7 neutrons) when one of the neutrons loses a high-energy electron (a beta particle β-) and converts into a proton.

Age of Earth: Radiometric age dating Decay equation: dN/dt = λNo also written as N=Noe- λt where λ is the “decay constant”. Half-life: time for 50% of atoms to decay When N=0.5xNo, 0.5No=Noe- λ t; ln0.5=- λ t t = ln0.5/- λ = ln2/ λ = t1/2 14C has a half-life of 5,730 years, so if there were 10,000 atoms of 14C in a sample today there would be 5,000 atoms left after 5,730 years, and 2,500 atoms left after 11,460 years. t1/2=ln2/ λ, then λ = 0.693/5730=1.21e-4 y-1

Radioactive Decay To view this animation, click “View” and then “Slide Show” on the top navigation bar.

Human evolution: at least 1,000,000 years Geologic time scale Fig. 1.H

Origin of Earth’s atmosphere Partial melting resulted in outgassing about 4 billion years ago Similar to gases emitted from volcanoes Mainly water vapor Carbon dioxide, hydrogen Other gases such as methane and ammonia

Origin of Earth’s oceans Water vapor released by outgassing Condensed as rain Accumulated in ocean basins About 4 billion years ago

Ocean salinity Rain dissolves rocks Dissolved compounds (ions) accumulate in ocean basins Ocean salinity based on balance between input and output of ions Ocean salinity nearly constant over past 4 billion years

Life in oceans Earliest life forms fossilized bacteria in rocks about 3.5 billion years old Marine rocks Life originated in oceans?

Stanley Miller’s experiment Organic molecules formed by ultraviolet light, electrical spark (lightning), and mixture of water, carbon dioxide, hydrogen, methane, and ammonia

Fig. 1.16a

Types of life forms Heterotrophs (most bacteria and animals) Autotrophs (algae and plants) Anaerobic bacteria (chemosynthesis) Photosynthetic autotrophs Chlorophyll captures solar energy

Photosynthesis and respiration Fig. 1.17

Oxygen crisis Photosynthetic bacteria release oxygen (O2) to atmosphere About 2 billion years ago, sufficient O2 in atmosphere to oxidize (rust) rocks Ozone (O3) builds up in atmosphere Protects Earth’s surface from ultraviolet solar radiation

Oxygen crisis About 1.8 billion years ago, most anaerobic bacteria killed off by O2 rich atmosphere Photosynthetic organisms created today’s O2-rich atmosphere O2 makes up about 21% of gases in modern atmosphere Large animals thrive

01_18

End of CHAPTER 1 Introduction to Planet “Earth”

Table A1.1

Figure A2.1

Figure A3.1

Figure A3.2

Figure A4.1

British Naval Power British Isles dominant naval power from 1588 to early 1900s Spanish Armada 1588

01_04

01_F

Fig. 1.1

Comparison of elevation and depth Average depth 3729 m (12,234 ft) Average elevation 840 m (2756 ft) Deepest ocean Mariana Trench 11,022 m (36,161 ft) Highest mountain Mt. Everest 8850 m (29,935 ft)

The Seven Seas Smaller and shallower than oceans Salt water Usually enclosed by land Sargasso Sea defined by surrounding ocean currents N and S Pacific, N and S Atlantic, Indian, Arctic, Antarctic

Physical properties Lithosphere Asthenosphere Mesosphere Outer core Inner core

Fig. 1.19